Known disk drives include a disk drive that uses various media such as optical disks, magneto-optical disks, or flexible magnetic disks. Among them, hard disk drives (HDDs) have come into wide use as the storage device of computers, and have become a storage device that is indispensable for the present computer systems. The application of HDDs is becoming wider and wider because of their excellent features not only for computer systems but also for moving-picture recording and reproducing apparatuses, car navigation systems, and as removable memories for use in digital cameras.
HDDs are equipped with a magnetic disk on which data is stored and a head slider for accessing the magnetic disk. The head slider includes a head device for reading and/or writing data from/to the magnetic disk and a slider on which the head device is provided. HDDs further include an actuator for moving the head slider to a desired position on the magnetic disk. The actuator is driven by a voice coil motor (VCM) to rotate about the rotation axis, thereby moving the head slider in the radial direction on the rotating magnetic disk. Thus, the head device section gets access to a desired track on the magnetic disk, and reads/writes the data.
General HDDs change the write current of the head device portions with temperature. The holding power of magnetic disks decreases as temperature increases. The amount of projection of the head device portion to a magnetic disk increases with an increase in temperature, and thus, the distance between the head device portion and the magnetic disk decreases with an increase in temperature. Therefore, write current is generally set so as to decrease with an increase in temperature.
Write currents relative to temperatures are determined in consideration of short writing due to current shortage, adjacent track interference (ATI) and so on. In other words, write currents are set so as to allow necessary writing (magnetization transition) on a target data track and not to erase data written in adjacent data tracks.
Furthermore, write currents are optimized for each head device portion so as to absorb variations in the performance of the head device portions (for example, refer to Japanese Patent Publication No. 10-334402 (“Patent Document 1”). Specifically, head device portions actually write data at different temperatures, and the written data is read by the head device portions. Accordingly, writing characteristics such as an overwrite characteristic and an error rate are measured at different temperatures. Thus, a write current at which an optimum overwrite characteristic and the error rate are provided at each temperature, is determined in consideration of the head disk contact and ATI.
To make a correct determination of the write current relative to temperature for each head device portion, it is preferable to measure the writing characteristics of each head device portion at different temperatures in an HDD operating temperature range. However, it needs much time and many facilities for measuring writing characteristics at different temperatures in the process of manufacturing HDDs.
On the other hand, another method can be provided in which one temperature is selected from a plurality of temperature ranges such as a low temperature range, a normal temperature range, and a high temperature range; writing characteristics are measured at the selected temperature; and the optimum write current at the selected temperature is used at another temperature in the corresponding temperature range. However, it is difficult for this method to set a write current for each temperature. Accordingly, an efficient and appropriate method for determining write current settings relative to temperatures for each head device portion is required.